Origen

The words metal and mettle (early 17th century) were once the same. Both could refer to a physical material and to a quality. In the 17th century the quality came to be particularly ‘vigour, spiritedness’, originally of horses but later also referring to people. By the mid 18th century the form mettle was being restricted to this, and metal to the material. Their ultimate origin is Greek metallon ‘mine, quarry, metal’.